In an automatic transmission disclosed in Patent document 1, in determining whether or not engagement of an engagement element starts, the determination is made based on information on whether a turbine rotational speed has reduced by a predetermined rotational speed as compared to the turbine rotational speed at a neutral range (hereinafter referred to as “N range”). And then, when it is determined that an inertia phase has started, an engagement pressure, which is supplied to the engagement element, is increased, and thus a transition to a completely engaged state occurs, thus achieving a smooth shift.
However, even though the inertia phase has not yet been started, there is a case where it is erroneously determined that the turbine rotational speed has reduced. In such a case, when the engagement pressure of the engagement element is increased, the engagement element is abruptly brought into engagement, and thus large torque fluctuations occur. This leads to the problem such as uncomfortable feeling given to the driver.